PassLabs Aleph 60 Owners manual

Volksamp

Pass Aleph 60 Owner's Manual

Dear Customer,
The Pass Aleph 60 is the part of the second generation of Aleph single-ended Class A power

amplifiers. This design results from my commitment to create the best sounding product, a
simple circuit having the most natural characteristic. The Pass Aleph 60 integrates power
Mosfet devices and pure single ended Class A operation in a simple two-gain-stage topology
with the sole purpose of recreating subjectively natural sound.

The Pass Aleph 60 is unique in a number of ways:
Most amplifiers on the market have between five and seven gain stages in series between the

input and the output. The Aleph 60 has but two, and enjoys a very direct path from input to
output, further enhancing the purity of the circuit and the resulting sound.

The output stage of the Aleph 60 is a unique blend of traditional design and innovation
addressing the unique requirements of loudspeakers. Previous methods of loading the output
stage have used networks consisting of resistors, coils, transformers, and active current
sources, all of which offer an optimal load line based on a resistive load. The Aleph 60 has a
current source topology which optimizes performance for a wide range of impedance and
reactance in the load, improving all aspects of performance into real loudspeakers. Pass
Labs has US patent No. 5710522 on this output stage topology.

The Aleph 60 is unique in that there are no adjustments of any kind in the circuitry. There are
no potentiometers to adjust. The operating parameters of bias currents and DC offset and so
on are defined by physical constants, and will not go out of adjustment.

Most important, the Aleph 60 brings improvement to the recreation of subjective sonic reality.
The amplifier delivers detail and subjective space rarely found in semiconductor circuits,
coupled with the authority and clarity rarely found in tube amplifiers.

The Pass Aleph 60’s ancestry lies in the highly praised Aleph 2. We have kept virtually all of
the circuit design and choice of parts intact, and the output wattage rating has been adjusted
to the smaller heat sinks.

The balanced input circuitry is the same topology as the rest of the original Aleph series,
accomplishing true high performance balanced input without additional active components. It
has been improved, however, to offer a higher input impedance on the single-ended input, 47
Kohms. The original Aleph 2 had a 10 Kohm input impedance.

The input devices are the same as the originals, but significant improvement is to be found in
the manner of matching the input devices. Previously the input differential transistors were
merely matched to each other, but beginning with the Aleph 30 and 60 they are now matched
both to each other and to the rest of the amplifier circuit. We select the input devices as part
of the complete amplifier, swapping them in and out until the best performance is achieved.
Tweaking the input stage in this manner and with other adjustment techniques we have been
able to significantly lower the noise floor and improve the power supply noise rejection of the
amplifier.

The Aleph 60 uses 12 output devices, the same as in the original Aleph series, and are
matched in the same manner, taken from the same lot codes and matched to about 2% Vgs.

The power supply incorporates much improved line noise filtering in both differential and
common mode, which filters out incoming noise and reduces noise emission by the amplifier.
The Aleph 60 uses 12 computer grade power supply capacitors for 120,000 uF of capacitance
and a 600 watt toroidal power transformer.

One of the biggest differences in the Pass Aleph 60 is the type of chassis and heat sink used.
The Aleph 2 was machined entirely from aluminum extrusions stock. While this resulted in a
unique and very functional appearance, it had several drawbacks. First it was very expensive.
Also, it allowed very limited space for access to input and output terminals on the rear of the
amplifier, and required the on/off power switch to sit in the rear underneath the wiring. It has
been said that ownership of the original Alephs was proof of the owner’s dedication to sound
at the cost of convenience.

The Aleph 60 has a new, more conventional, chassis with heat sinks on the side, a faceplate
with a power switch, and a regular sheet metal type chassis. In addition to being more
convenient, this approach costs less, and we have passed the difference on to the customer.

The final result is that the Aleph 60 performs slightly better than the original Alephs and costs
less.

The Volksamp version of the Aleph 60 is produced under license from Nelson Pass and Pass
Laboratories Inc., and is distributed and serviced by Pass Labs Domestic Sales Inc. and Pass
Labs Foreign Sales Inc.

Thanks you for purchasing it. Enjoy.

Nelson Pass

( [e-mail] )

Setup

The amplifier has four connections and one switch: The first connection and switch is the AC
line power system. The amplifier's voltage and current rating are indicated on the bottom. It
will be either 240 volts, 120 volts, or 100 volts, all with a 3AG slow blow type fuse. The
frequency rating of the AC line source is 50 to 60 Hz.

Your amplifier is provided with a standard AC power cord which fits into the line receptacle
located just below the power switch. The amplifier is equipped for operation with an earth
ground provided by the AC outlet. Do not defeat this ground. The chassis of the amplifier is
connected directly to this earth ground, and the audio circuit ground is connected to the
chassis and earth through a power thermistor, which gives a ground safety connection but
helps avoid ground loops.

The second connection is the single-ended input, which occur through a standard RCA
connector. The input impedance of the amplifier is 47 K ohms, and is DC coupled, with no
capacitors.

The third connection is the balanced input, which occurs through a standard XLR connector.
The balanced input impedance is 52 Kohms. Input pin 1 of the XLR connector is input
ground, pin 2 is the positive input, and pin 3 is the negative input. As shipped, there is a
shorting jumper between pins 1 and 3, which is the configuration for single-ended input.

This shorting jumper should be used when operating the amplifier with the RCA input,
otherwise you will not get the proper gain figure for the amplifier. If you operate the amplifier
with balanced inputs, you will remove this jumper, and we advise you to save it carefully for
future use.

The fourth connection is the amplifier output connection. Connect the 5-way output connector
to loudspeaker plus and ground, using the cable of your choice.

The amplifier draws about 240 watts from the wall at all times, and during idle operation nearly
all of this energy will appear as heat on the heat sinks. Good ventilation is vital to the proper
operation of the amplifier. It has been adjusted for optimal performance at room temperature,
but will work well between 50 and 90 degrees Fahrenheit (10 to 33 Celsius). You should
leave at least six inches clearance on the sides and top. The amplifier should not be placed
in a closed cabinet which does not have forced air ventilation.

This amplifier runs hot. The heat sinks will warm up in about an hour to a temperature which
will not be comfortable to touch for more than a moment or two, which is 120 to 130 degrees
Fahrenheit (50 to 55 degrees Celsius). This is normal, and there is a thermal shut off system
which will shut down the amplifier at internal temperatures in excess of 160 deg. F. and 70
deg. C.

It takes about an hour of warm up time to get the best performance out of the amplifier. It will
take that long to reach operating temperature and exhibit lowest distortion and noise. This is
not a subjective judgement, but based on actual distortion and noise measurements. Many
customers have reported that longer warm up yields more improvement.